John B.
Yelp
I'm confining this review to the museum itself, and not reviewing the rest of the building or the separate Metrolink station.
What's there is good if you're interested in trains, history, or the local area. If you live somewhere else, you can take a Saturday morning Metrolink train to the San Bernardino station, tour the museum, and then take a return train.
My mistake was in planning a 2 1/2 layover to visit the museum. Despite touring all of the exhibits and spending time talking with one of the volunteers, I was pretty much done in an hour. That gave me an hour and a half to visit a Subway across the street, eat lunch, return to the station, read several Amtrak schedules, and wait. Although I've never seen any trouble in the area in my two visits there, this area has been identified as "sketchy" and not a place to really walk around.